1. Field of the Invention
This invention relates to long-term, drop-in-tank lavatory sanitizing materials and to methods for making and using such materials.
2. Description of Related Art
One well-recognized source of germs in modern households is the toilet. Consumers spend considerable time and money in cleaning and sanitizing toilets. Not only is this difficult task unpleasant for many people, it also does not protect against proliferation of germs between cleanings.
One alternative to continual cleaning of the toilet is the use of in-tank articles that dispense a sanitizing agent into the toilet tank. These articles employ a chemical or combination of chemicals that release a halogen containing sanitizing agent when in contact with water. These articles have the advantage of providing continuous cleaning and sanitizing of the toilet, at least while the sanitizing agent remains in the tank.
If the release of the sanitizing agent is uncontrolled, the high equilibrium concentration of the halogen containing sanitizing agent may harm the tank itself and the equipment exposed to the halogen containing sanitizing agent in the tank. In order to control the halogen release rate, thereby controlling the harmful effects of uncontrolled release of the halogen into the tank, the halogen containing sanitizing agent is usually contained within some type of a dispensing system such as a container or a metering device.
One advantage of a container or metering device is that the useful life of any given unit of the halogen containing sanitizing agent is extended. Dispensing systems, however, are inconvenient, messy and must be removed from the tank and disposed of when the chemicals are exhausted. This disposal is unpleasant and can reduce the efficacy of germ killing by discouraging the consumer from replacing or replenishing exhausted supplies of the sanitizing agent.
Use of a product that can be simply dropped into the tank will eliminate the dispenser, but such a product reintroduces all of the problems that the dispenser was designed to circumvent. For instance, dispensers control the release rate of halogen containing sanitizing agent in three basic ways: they limit the quantity of water in contact with the agent; they limit the surface area of the material containing the agent exposed to the water; or they regulate the release rate of dissolved halogen containing sanitizing agent by controlling the release rate of the water containing the agent into the body of the tank. Without the container or dispenser, all of the water within the tank can come into contact with the entire exposed surface area of the chemicals.
Designing a drop-in product that releases the halogen containing sanitizing agent over a period of several hours is feasible. However, formulation difficulties increase rapidly as the active life of the product increases. In addition, the water in toilet systems does not flow continuously so maintaining rate of release within a constant range offers additional difficulties. The difficulty of obtaining a controlled, substantially constant rate of halogen containing sanitizing agent release, for example in the preferred range of the invention of about 0.5 to about 5 ppm, increases exponentially as the useful life increases beyond a time of about 1 week. Nevertheless, consumers do not wish to replenish a drop-in lavatory cleaning block constantly. Rather, consumers desire a product that only needs to be replaced after at least about 2 months, and preferably about every 3 to 4 months of use.
Consumers also have individual preferences for the duration of the toilet block. Some consumers prefer replacing the block every four months, for convenience, while others prefer changing the block about every two months so that it is easier to remember to replace the block. One simple way of regulating the duration of a block is by making the block bigger or smaller, so that the block will dissolve more or less quickly. Changing the size of a block, however, is not as simple as it seems. Changing the size of the block can change the release profile of the halogen containing sanitizing agent because of the change in block surface area.
Others have tried to regulate the release rate of a halogen containing sanitizing agent, with varying degrees of success. U.S. Pat. No. 2,863,800 to Gottfried, issued Dec. 9, 1958, for example, is directed to a composition for increasing the dissolution rate of 1,3-dichloro-5,5-dimethyl hydantoin (a halogen containing sanitizing agent) in water. The solution for obtaining maximum solubility "within a matter of seconds" offered in that patent is the addition of a comminuted wetting agent. One of the formulations discussed in that patent comprised 280parts by weight 1,3-dichloro-5,5-dimethyl hydantoin, 300 parts by weight NaCl, 360 parts by weight Na.sub.2 SO.sub.4, 50 parts by weight NaH.sub.2 PO.sub.4, and 10 parts by weight of a series of wetting agents. The patent also mentions that the tendency of the formulation to form "wet, gummy masses" is avoided by the addition of sodium or potassium chloride. Anhydrous sodium sulfate, although a useful material for retarding moistening of the composition during storage, cannot act as a substitute for sodium chloride in the composition.
Another patent, U.S. Pat. No. 5,178,787 to Hung et al., issued Jan. 12, 1993 is directed to a toilet cleaning block that releases a halogen containing sanitizing agent in a controlled, substantially constant rate for about 2to about 4months of constant contact with water. Although the results obtained by practice of this patent are excellent, the combination of about 4% to about 10% aluminum hydroxide and about 90% to about 96% halogen containing sanitizing agent is expensive.
Accordingly there is still a need in the art for a formulation that can deliver the performance obtainable from U.S. Pat. No. 5,178,787 to Hung et al, without the associated cost. The formulation should also be able to provide a reliable mechanism for tailoring useful life of the product to individual customer preferences without the need for reformulation.